Liberal Democrats today urged Labour supporters to back them and stop Conservatives being elected to the Welsh Assembly.

The Lib Dems claimed that if people cast both their votes for Labour candidates, Tory AMs could get in by the back door because of the proportional representation electoral system.

The electoral system used for the Assembly election gives everyone two votes, one for a constituency AM and one for a party on the regional list.

Lib Dem Assembly leader Michael German said that at the 1999 election, 361,657 people "wasted" their second vote for Labour because it meant eight Tories won Assembly seats.

Under the Assembly system, votes in the second ballot are used to allocate seats to parties according to the general level of support, but penalises parties which have already won lots of seats.

Parties which win lots of constituency seats under the first ballot will not get many Additional Members. Parties which receive lots of votes but do not win many constituency seats are likely to do well in getting Additional Members.

Mr German told a press conference at the party's head office in Cardiff Bay: "A lot of people did not get the result they wanted last time.

"It is very difficult for people to understand the system and how to ensure they do not elect Conservatives.

"By voting Labour twice people let the Tories in. If Labour voters want to stop Iain Duncan Smith's Tories the best way to do it is to vote for the Welsh Liberal Democrats on the big ballot paper.

"Wales has rejected the Conservatives at Westminster they have no MPs in Wales. Wales has rejected the Conservatives in local government they have fewer councillors than any other party.

"Next Thursday Wales has the chance to reject the Conservatives in the Assembly too."